When you activate something for 500 million accounts, it automatically takes on significance. The move by Facebook to add location-based service to its network is a sign the concept has arrived to the mainstream.

Facebook calls its service Places and it permits check-ins at a variety of, well, places. It strives to help you understand more about your Facebook friends' preferences and traits of consumption and activity.

It complements, rather than competes with, existing services like Foursquare and Gowalla, and its implications for journalism are not revolutionary as much as they're further impetus to get in the game.

While check-ins are bound to become a commodity in the time ahead --- particularly as services provide it more readily --- the rich stream of data that comes from them will be very useful for all companies in the information business.

Journalism will benefit in understanding more about events and places from the user base willing to give access to their locations. But the stream of behavioural data will be even more important.

Foursquare, the location-based information service, surpassed two million users today.

It still isn't as large as some other location-based services but appears to have the sharpest growth pattern (it only surpassed one million users three months ago). Its flexibility as a tool and its system of recognition and rewards appears to have struck a chord.

Newsrooms need to consider it seriously, without a doubt. Even if it requires a fair amount of management to keep your location updated, and even if it raises some questions about privacy and security, there are ways to implement Foursquare without running risk.

1. Finding a source with a specific tie to a location.2. Finding a source on the scene.3. Finding out where your contacts are.4. Alerting audiences to the location of news.5. Providing tips on locations.6. Learn about a place.7. See where people are.8. Say where you are.

It is only the last point that concerns some news managers, who aren't sure disclosing location is safe for journalists and who also wonder if their competitive advantage might be surrendered by alerting people where certain information resides.

That said, if we are into an era increasingly of location-based media, the media will increasingly have to understand the location-based entities.

Location-based journalism is still a little confusing to newsrooms typically reticent about publicizing their newsgathering, but Mashable has a good guide on seven tips for journalists.

The focus is Foursquare but could just as easily be Gowalla or any of the services. Contributors Shane Snow and Vadim Lavrusik identify ways in which newsrooms can benefit, and even if they seem a little marginal as ideas of the moment, they are bound to grow as the services grow.